Free Radical Beam Source

A source of pure beams of thermal alkyl radicals for molecular beam scattering experiments is described. A parent compound, (CH3)2Hg, (CH3)3Bi, CH3I, or (C2H5)2Hg, was pyrolyzed in an array of small Ta tubes, and a beam of the products entered a slotted disk type velocity selector. Selection at 1500 m/sec chemically purified the radical beam by removing parent molecules and high mass decomposition products. The best purities, found by modulated beam mass spectrometry, average to 94±8 mole% CH3, and in these runs the estimated intensities were 2−7×1015 radicals/sr·sec, or 3−10×1013 radicals/cm2·sec at the detector. Light hydrocarbons (C1,C2) were the major impurities, their concentration increasing with methyl flux.